A liquid crystal display (LCD) device is an appliance capable of controlling transmission/blocking of light (on/off of display) by controlling alignment of liquid crystal molecules having birefringence. A liquid crystal display device has, for example, an array substrate, a color filter substrate, and a liquid crystal layer sandwiched between a pair of substrates, that is, the color filter substrate and the array substrate. The surfaces of both substrates in the liquid crystal layer side may have an alignment film, each.
Hereinafter, one example of production steps for a liquid crystal display device will be described. A plurality of spacers made of an insulating material are formed on one of the above-mentioned substrates and both substrates are stuck to each other. In the case of employing an ODF (one-drop-fill) method, a liquid crystal material is dropped before sticking the substrates, and in the case of employing a vacuum injection method, a liquid crystal material is vacuum-injected after the substrates are stuck and the inject is closed. Thereafter, a polarizing plate and a phase difference film are stuck to the faces of the respective substrates in the reverse sides of the liquid crystal layer to complete a liquid crystal display panel. Further, a gate driver, a source driver, a display control circuit, etc. are mounted on the liquid crystal display panel and a back light unit or the like is combined to complete a liquid crystal display device.
In recent years, a technique for forming a polymer layer (PSA layer) capable of controlling orientation of liquid crystal molecules on an alignment film or on a substrate having no alignment film has drawn attention. A PSA layer is formed by sealing a liquid crystal composition obtained by mixing a polymerizable component such as a monomer, an oligomer, or the like with a liquid crystal material between substrates and polymerizing the polymerizable component by heat or light (e.g. ultraviolet) irradiation.
Patent document 1 discloses formation of an alignment retention layer by sandwiching, between both substrates bearing a photo-alignment film, a liquid crystal material obtained by mixing a photo-polymerizable compound, and polymerizing the photo-polymerizable compound by light irradiation. The photo-alignment film disclosed in Patent Document 1 is an alignment film containing a polymer having a main chain and a side chain including a photo-reactive functional group, and a plurality of regions for providing alignment regulation force in different directions for the alignment film are formed by irradiating the alignment film with light from different directions. Owing to the light irradiation, an impurity is sometimes generated from the photo-alignment film, but the impurity is immobilized by the alignment retention layer and generation of impurity ions in the liquid crystal layer is suppressed to fix the pre-tilt direction of liquid crystal molecules and at the same time to suppress decrease of voltage holding ratio and occurrence of image sticking.
Patent Document 2 discloses that image sticking of a liquid crystal display device can be lessened by injection of a liquid crystal composition containing a polymerizable monomer between substrates and irradiating with ultraviolet rays while applying voltage between transparent electrodes on the opposite to each other on the substrates to polymerize the monomer and that the monomer has one or more ring structures or condensed ring structure, and 2 functional groups directly bonded to the ring structure or the condensed ring structure.